In data communications, a data signal transmitted from a first modem to a second modem across a channel is often distorted due to the channel. In particular, the channel may cause intersymbol interference and other distortion. To remedy the distortion to a data signal due to the channel, it is often the case that an equalizer is employed in the receive circuitry of modems. In particular an equalizer may operate in the time domain or in the frequency domain.
Many equalizers that operate in the time domain employ digital signal processing techniques. Such time domain equalizers (TEQ's) may feature a digital filter with several coefficients which must be tuned to cancel the effects of a specific channel employed for data communication. The process of tuning these coefficients generally occurs at the startup of data communication.
To explain further, when TEQ training takes place, often times the transmitting modem sends a continuous data signal which comprises a predetermined data sequence that is repeated over and over. The same predetermined sequence is generated in the receiving modem, the sequence being repeated over and over in similar fashion to the signal received from the transmitting modem. The time domain equalizer generally employs various techniques to tune the coefficients of the digital filter applied to the received signal, thereby canceling the channel distortion so that the received signal matches the signal generated in the receiving modem.
In order to tune the coefficients, it is often the case that the received data signal and the generated data signal are first synchronized in time. When the predetermined sequence which is repeated in both the received and generated data signals is particularly long in nature, such as, for example, in discrete multitone (DMT) data communication, significant processing and memory resources are consumed to accomplish the required synchronization. Consequently, there is a need for a system and method of synchronizing a predetermined repeated data sequence contained in a received data signal and the same repeated data sequence contained in a generated data signal in a receiving modem where the predetermined data sequence is particularly long.